In a given space around the nucleus, only certain orbitals can exist. Each orbital of a stable energy state for the electron is described by a particular set of quantum numbers.

Each electron in an atom is described by a set of three numbers n, l, and ml .These numbers are called quantum numbers. These numbers indicate the probability of finding the electron in the space around the nucleus.

• What information do the quantum numbers provide?
      The quantum numbers describe the space around the nucleus where the electrons are found and also their energies. These are called atomic orbitals.
  

• What does each quantum number signify?

The principal quantum number is related to the size and energy of the main shell.
    ‘n ’ has positive integer values of 1, 2, 3,…
    As ‘n’ increases, the shells become larger and the electrons in those shells are farther from the nucleus.
    An increase in ‘n’ also means higher energy. n = 1, 2, 3, ... are often represented by the letters K, L, M… For each ‘n’ value there is one main shell.

‘l’ has integer values from 0 to n-1 for each value of ‘n’. Each ‘l’ value one sub-shell.
    Each value of ‘l’ is related to the shape of a particular sub-shell in the space around the nucleus.
    The value of ‘l’ for a particular sub-shell is generally designated by the letters s, p, d . . . as follows:

When n = 1, there is only one sub-shell with l = 0. This is designated as ‘1s’ orbital.

    When n = 2, there are two sub-shells, with l = 0, the ‘2s’ sub-shell and with l = 1, the ‘2p’ sub-shell.